It is 347cc and mine turns the scale 28"O.D.x 25"pitch propeller at 3000 rpm with ease.
The difference between a rotary and a radial engine is that the rotary engine propeller is fixed to the front of the engine and the crankshaft protrudes from the rear and is fixed to the aircraft, the whole engine rotates with the prop. An engine known as a "radial" has the engine fixed to the aircraft and the propeller attached to the crankshaft where it protrudes from the front of the engine.



Metal was first cut in August 2004 and it first ran on Jan. 9th 2008. It varies from the full size in that I designed a gear pump for the oil supply, it has electronic ignition and a Walbro carburettor. The original-style valve springs of the conical wound flat spring type were unsuccessful so it now has conical wound piano wire ones which so far work well. I took many photographs of a full size example at the Shuttleworth Collection, Old Warden ( engine now at RAF museum, Cosford) and the makers plate which I have had replicated by photo etching gives a date of Nov.1917, No.1 so it must be a prototype before the 1918 production runs.



I actually received a nine nameplate strip from the photo etcher so I will be fitting another sometime. I'm not happy with my letter punching, even 'though they are only 1mm high! The nameplate measures 20mm x 10mm.



It has a total loss oil system as the oil eventually combines with the petrol in the crankcase before entering the induction chamber. The exhaust is to atmosphere straight from the exhaust valve ports.
All parts were made on my Myford ML7R 3.1/2" lathe and a Wabeco F1210E vertical milling machine including the 1sq.mm section piston rings cam gears and ring gears which operate the valve tappets. The valves are stainless steel and just seat in the mild steed cylinderheads. I decided I wanted reliability so used commercially available miniature spark plugs at £9 each from Paul Knapp, Oregon, USA which probably compares to modern car plugs. The carbon brush for the distributor disc came free from a used Phillips CT scanner brush block and a reserve one comes from a Peugeot cooling fan (I think).
The induction pipe top elbows and lower sockets were cast for me by a friend (VERY good friend, he did a great job) in the model engineering club I belong to. The ignition system started life as a TIM-6 unit, again from the States, assembled for me by Kees Blockland and a 2m/s triggering device added by Martin Fullick.





The grand opening of the W.O.Bentley Memorial building near Banbury in Oxfordshire on July 1st 2007. The engine was exhibited in an unfinished condition in the foyer and HRH Prince Michael of Kent who opened the building showed a great deal of interest as he was unaware that Bentley had any connection with aero engines.




The plane I will be building is to be a stable platform and be as safe as possible for the engine is a 1/4 scale Avro 504 which I will be building from David Boddington plans. One desirable thing about this aircraft is the large skid which protrudes in front of the propeller which should, I hope, protect the engine as much as possible, especially preventing nose-over's on landing. Boddo's design is centred around a Zenoah 62, which I have, so the intention is to design the front end to take either engine. I would ballast the plane as if the Bentley were in it and fly it with the Zenoah to set up and prove the airframe, then change engines!!


Just as an aside, the engine ran extremely well when initially started in January, one reason was that the ignition system gave very long high oscillating frequency sparks which guaranteed combustion. This was modified by Martin and it now has a normal spark and will benefit from a variable advance and retard system which I hope to have servo operated, linked to the TX throttle when in the plane.

Andy Johnston
2 May 2008